I can't really add much, as I believe Coach May and some of the others have hit the nail on the head, but I do have a couple little things to offer. What is your son's long term goal? Does he want to play in college? If so, his HS soph playing time won't have a lot to do with that. But his grades will. His club team will. His work ethic will.
In 6th grade, my 2015 set a goal to make varsity as a freshman. I'm happy to say he accomplished that goal and has been a V starter since the 3rd game of his freshman year. As a freshman, he set the goal of playing in college. I'm happy to say he has signed a scholarship to play in college. To achieve these goals, above all, he worked extremely hard - on and off the field. He's never had a drink or smoked anything. He's never been in any trouble. He also knows the importance of good grades. And you know what, the first question every college coach he worked out for wasn't "How much playing time did you see in HS?" It was "What'd you get on your ACT?"
I know it's hard for a soph to sit. I know it's hard for a mom to watch. Try to look at the big (long term) picture. Focus on grades, too. And help in the ways you can. Not to toot my own horn, but I happen to be a phenom as a front-tosser. Every day, after a three hour practice, I front toss at least 100 balls to my son. If it's dark or bad weather, I set more than that on a tee in the garage. Every night. In season and out. I'm there to listen, and have sat through enough workouts to offer some advice on little tweaks.
Be supportive and don't talk to the coach. Look at the big picture and focus on the long term goal. Everything will fall in to place.